Obesity and dietary imbalance

From a blocked artery to a heart attack

Step through it one stage at a time.

1. 1The supply lineThe coronary arteries surround the surface of the heart and supply the heart muscle with blood. That blood carries oxygen and glucose, the fuel for cellular respiration, which gives the heart muscle the energy to contract.
2. 2Fatty tissue builds upIn coronary heart disease, a build-up of fatty tissue inside a coronary artery leaves a narrower space for the blood to pass.
3. 3Blood flow dropsWith a narrower space, the blood flow is reduced. If the arteries are blocked, not enough blood flows through them.
4. 4Heart attackThe heart muscle cells no longer receive the oxygen and glucose they need for cellular respiration. They stop contracting and die. That's a heart attack.
5. 5Cardiac arrestIf a large enough proportion of the heart is damaged, it can cause cardiac arrest and potentially death.

What you need to know

• We use energy for movement, growth and even sleeping, and age and activity change how much energy we need.
• Fat is an important part of our diet: it's a store of energy and it's used to make cell membranes.
• Have a goYour cousin announces: "Fat is useless, the less the better!" Which two jobs of fat can you throw straight back at them?

  It's a store of energy, and it's used to make cell membranes.

  The tempting answer treats all fat as bad, but fat is an important part of our diet with both of those jobs.

• Food we no longer need for energy is converted into fat, so a person might gain body fat and could become obese.
• Ultra-processed foods are often very high in saturated fat, sugar or both, which can imbalance energy in and energy out.
• BMI compares weight and height: body mass in kilograms divided by height in metres, squared.
• Have a goSomeone is 150 cm tall. Which number goes into the BMI formula for their height, and what happens to it?

  1.5 (metres), then it's squared: 1.5 × 1.5 = 2.25.

  The formula wants metres (100 cm is 1 m), so using 150 would make the BMI come out far too small.

• Adult categories (not used for children): under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30 or above obese, 40 or more severely obese.
• BMI compares weight with height, so a muscular sports person can score overweight or obese without much body fat.
• Have a goTwo adults are the same height and have the same body mass, but one is very muscular. Same BMI? Same amount of body fat?

  Same BMI. Not necessarily the same body fat.

  BMI only uses weight and height, so it can't tell heavy muscle from fat.

• Waist-to-height ratio divides waist by height, and 0.5 or higher means increased risk. Skinfold calipers estimate body fat percentage.
• Obesity is linked with type 2 diabetes, coronary heart disease, some cancers, stroke and depression.
• In coronary heart disease, fatty tissue narrows a coronary artery, cutting blood flow to the heart muscle and risking a heart attack.

The big picture

Obesity starts with an energy imbalance: when more energy goes in than the body needs, the food it doesn't need as energy is converted into fat. BMI compares weight with height to put an adult into a category, but it can't tell muscle from fat, so other measures help. Obesity is linked with several health conditions, including type 2 diabetes and coronary heart disease.

⚠ Watch out

Thinking BMI measures body fat. It only compares weight with height, so a muscular sports person can score overweight or obese without much fat. And when you calculate it, remember the height has to be in metres before you square it, not centimetres.

Memory hook

BMI weighs you against your height, not your fat.

Check yourself

Without looking back, explain the whole chain in your own words, from energy in to obese. Use: energy used, converted into fat, body fat, BMI. Then add one sentence on where ultra-processed foods fit in.